1. Field
The disclosure relates to techniques for providing amplifiers with adjustable gain.
2. Background
Amplifiers with adjustable gain are commonly utilized in many types of circuitry, e.g., in wireless transceivers including a power amplifier for amplifying a signal for transmission over a wireless medium. To provide adjustable gain, a composite amplifier may be implemented using a plurality of individual amplifiers coupled in parallel, wherein each of the plurality of amplifiers may be turned on or off to vary the effective size of the composite amplifier. A common amplifier topology is a multi-stacked cascode circuit, in which an input transistor is coupled to at least two cascode transistors. To turn off an amplifier adopting a multi-stacked cascode circuit topology, the gate bias voltages of the cascode transistors may be grounded to turn off the DC bias current through the amplifier.
A disadvantage of grounding the gate bias voltages in this manner is that, while the selected amplifier may be effectively turned off, large voltage drops may still appear across the terminals of the turned-off cascode transistors. This is due to the operation of the other amplifiers in the composite amplifier that are still turned on, and which may still the drive the output node. In certain cases, the large voltage drops may exceed the breakdown limits of the turned-off devices, thereby undesirably increasing the failure rate and/or cost of the composite amplifier circuit.
It would be desirable to provide improved techniques for adjusting the gain of an amplifier.